A Wide Area Network (WAN) which employs an Internet Protocol-Virtual Private Network (IP-VPN) technique or the like is generally used as a communication network between bases, used for cloud computing or the like.
In a case where a terminal present in a certain base communicates with a terminal present in another base, the communication is performed via a line which connects a self-base Local Area Network (LAN) to a WAN and a line which connects the WAN to another base LAN. In these lines, an available bandwidth is restricted depending on contract bandwidths.
In communication between terminals, a Transport Communication Protocol (TCP) is generally used. In the TCP communication, data is transferred via a transmission buffer of a transmission terminal and a reception buffer of a reception terminal. An application which operates in the transmission terminal writes data to be transmitted in the transmission buffer. The transmission terminal carries the data written in the transmission buffer in a packet which is transmitted to the reception terminal. When the packet is received from the transmission terminal, the reception terminal accumulates the received data in the reception buffer. In addition, an ACK packet in which a sequence number indicating an end of the received data which has been arranged and a remaining capacity of the reception buffer are described is returned to the transmission terminal. When the ACK packet is received, the transmission terminal determines the received data from the described sequence number and deletes the data from the transmission buffer. An application which operates in the reception terminal periodically reads the received data which has been arranged and accumulated in the reception buffer, and deletes the read data from the reception buffer. Each terminal has a set of the transmission buffer and the reception buffer for a single TCP communication item, and writes data in the transmission buffer in a case of transmission and reads data from the reception buffer in a case of reception.
PTL 1 discloses a method of controlling the size of data accumulated in a transmission buffer or the size of data which can be newly accumulated, based on a value of a congestion window size.
PTL 2 discloses a method of controlling a data size of a buffer based on a multiplication value of a bandwidth and communication delay.